Overview
The CCHA power analysis evaluates the effect of reducing sampling effort for vegetation transects at all long-term monitoring sites in Tampa Bay. Currently, sampling is conducted every half meter and the power analysis evaluates the effect of reduced effort up to sampling every ten meters, or a 95% reduction from the current effort. Scenarios evaluating more than 50% (1 meter sampling) or 66% (1.5 meter sampling) reduction in effort are unrealistic, but still useful to understand the effects on quantitative measures of habitat. These measures include:
- Total species richness at a site
- Total species richness at a site by vegetation zone
- Species frequency occurrence at a site
- Species frequency occurrence at a site by vegetation zone
- Vegetation zone distances by site
- Elevation range at which 95% of key species occur (e.g., mangroves)
The relative reduction in effort associated with each half-meter increase along a transect is shown below.
Sub-sampling scheme
All existing CCHA vegetation surveys were sub-sampled from the existing effort of sample plots every half meter. The plot below shows an example of the sub-sampling scheme, where effort was reduced in increments of a half meter, starting from the complete survey to an upper limit of sampling every ten meters. For simplicity, the plot shows sub-sampling up to every three meters for a hypothetical 30 meter transect (transect exceed 100 meters at all site).
The existing surveys were sub-sampled at the specified meter interval for every unique subset (or replicate) that was possible. For example, two unique replicates can be created with sub-sampling every one meter, three every 1.5 meters, etc.
The large red points show which of the existing survey points were sub-sampled for the specified sub-sample distance. For each site and sample year, the vegetation transect was sub-sampled following the scheme below (sub-sampling up to ten meters) and relevant habitat summaries were estimated. The top row represents the complete transect, or the “truth”.
